During photosynthesis, plants convert light energy into electrochemical energy, and eventually into chemical potential energy stored in carbohydrates and other compounds. The carbohydrates are oxidized as needed to provide energy to the organism. A new approach to mimicry of the photosynthetic process that involves a dye-sensitized nanoparticulate semiconductor photoanode working in combination with an enzyme-catalyzed biofuel cell is described in Gust et al., “Enzyme-based Photoelectrical Cell for Electric Current Generation” (WO 03/079480). This system achieves simple and direct coupling of the two complementary processes, combines some of the advantages of each approach in a single unit, and can in principle provide more power than either process working independently.
The present inventors have now shown that this system can be used to detect and quantitate NADH/NAD+ and/or NADPH/NADP+ as well as NADH/NAD+ and/or NADPH/NADP+ dependent enzymes.